Problem: $\text D = \left[\begin{array}{rr}-1 & -2 \\ -2 & -1\end{array}\right]$ What is the determinant of $\text D$ ?
The determinant of a 2x2 matrix can be computed the following way: $ \left|\begin{array}{rr}a & b \\ c & d\end{array}\right| = (a \times d)-(b \times c) $ In this specific case, $ \left|\begin{array}{rr}-1 & -2 \\ -2 & -1\end{array}\right| = (-1 \cdot -1)-(-2 \cdot -2) $ $ = -3 $